Orforglipron (Foundayo) vs Tirzepatide (Mounjaro): Comparison

Tirzepatide, sold under the brand name Mounjaro, is currently the most effective approved weight loss medication in the UK. But the landscape is changing fast, with new oral GLP-1 weight loss pills offering similar benefits without injections.

One of them is orforglipron, sold under the brand name Foundayo, which is now approved in the UK. It's made by the same manufacturer as Mounjaro (Eli Lilly), but it isn't a "Mounjaro pill", it's a distinct medicine with a different active ingredient. Here's what the evidence shows.

Key Takeaways

• Orforglipron is a once-daily GLP-1 pill, now approved in the UK under the brand name Foundayo
• Tirzepatide (Mounjaro) is a weekly injection targeting both GLP-1 and GIP
• Over 72 weeks, tirzepatide achieved up to 22.5% weight loss vs 12.4% for orforglipron at the highest approved dose
• Both have similar digestive side effects like nausea and diarrhoea, which usually ease over time
• Both Mounjaro and orforglipron are available now through Voy

Orforglipron vs tirzepatide: What’s the difference?

What is orforglipron (Foundayo)?

Orforglipron, sold as Foundayo, is a once-daily weight loss pill. It's licensed in the UK for weight management and type 2 diabetes. It belongs to a family of medicines called GLP-1 receptor agonists, which includes injections like Wegovy and Saxenda, and the oral Wegovy pill. Unlike other oral GLP-1 medications, Foundayo can be taken at any time of day, with or without food.

What is tirzepatide (Mounjaro)?

Tirzepatide is the active ingredient in Mounjaro, a weekly injection also licensed in the UK for weight management and type 2 diabetes. It's currently the most effective approved weight loss medicine available. Tirzepatide works on two natural hormones (GLP-1 and GIP) rather than one, which contributes to its strong results.

Do orforglipron and tirzepatide work differently?

Yes. Orforglipron works by mimicking the effects of GLP-1, a natural hunger hormone. This curbs your appetite and makes you feel full, so you eat less.

Mounjaro does that too. It also activates another hormone, GIP, which enhances insulin release and may further support weight loss. This dual action contributes to Mounjaro's greater effectiveness in trials.

Orforglipron vs tirzepatide: weight loss results

Two key trials show the difference:

• In the ATTAIN-1 trial, people taking the highest approved 17.2mg dose of orforglipron lost an average of 12.4% of their body weight over 72 weeks.
• In the SURMOUNT-1 trial, people on the highest 15mg dose of Mounjaro lost up to 22.5% of their body weight over 72 weeks.

Tirzepatide produces greater weight loss at its highest dose, but orforglipron's results are still significant for a daily tablet.

Does orforglipron cause more side effects than Mounjaro?

There's no trial that has directly compared the two, but here's what we know from their separate clinical trials.

Both medications share the same most common side effects: digestive issues like nausea, vomiting, constipation, and diarrhoea, which are usually mild to moderate.

Discontinuation because of these gut-related side effects specifically is broadly similar between the two:

• Across different trials, 6.8% of people stopped taking orforglipron at the highest dose because of gut-related side effects.
• In the SURMOUNT-1 and SURMOUNT-2 trials, around 4.3% of people stopped taking Mounjaro because of its gut-related side effects.

These figures come from separate trials, so they aren't a direct comparison, but the overall picture is similar for both medicines.

Side effects support at Voy

"If you're using Voy and you experience any side effects, rest assured that our expert clinicians are just a message or phone call away. They can adjust your dose, prescribe medication to ease your symptoms, or simply offer reassurance.

Everyone responds differently to weight loss treatment and we'll help you find what feels right for you."

Phoebe Fox - Weight Loss Specialist

Orforglipron vs Mounjaro: dosing schedule

Both medications use a step-by-step dose escalation, starting at the lowest dose and increasing gradually if tolerated well. This helps the body adjust and reduces side effects.

Here's how the dosing schedules compare:

• Orforglipron (Foundayo) is a once-daily tablet with six dose levels: 0.8mg, 2.5mg, 5.5mg, 9mg, 14.5mg, and 17.2mg. Dose increases happen every 30 days, if tolerated.
• Mounjaro is a once-weekly injection with six dose levels: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, and 15mg. Dose increases happen every four weeks, if tolerated.

Foundayo can be taken at any time of day, with or without food. The tablet should be swallowed whole, not broken, crushed, or chewed. Mounjaro can also be injected at any time of day, on the same day each week.

Although Foundayo is a daily tablet, some people may prefer it to a weekly injection.

Can you switch from Mounjaro to orforglipron?

Yes. Now that orforglipron is approved in the UK, switching is possible, whether you're still in the active weight loss phase or have reached your goal weight and are looking for a maintenance option. The ATTAIN-MAINTAIN trial specifically looked at switching after weight loss, testing whether orforglipron could work as a maintenance treatment once someone has already lost weight on an injection.

In the trial, people who had already lost weight on Zepbound (the US version of Mounjaro for weight loss) or Wegovy were given either orforglipron or a placebo. After 24 weeks:

• People switching from Wegovy to orforglipron stayed at almost the same weight (0.1kg change), while those on placebo regained 9.4kg.
• People switching from Zepbound to orforglipron regained 2.6kg, while those on placebo regained 9.1kg.

This suggests orforglipron could work as a maintenance option once weight loss is achieved on injections like Mounjaro, helping prevent the significant weight regain that often happens when treatment stops.

Any switch, whether during active weight loss or for maintenance, should be discussed with your prescriber first.

Orforglipron vs Mounjaro: cost and UK availability

Mounjaro is the available option in the UK right now. You can get it on the NHS if you meet certain criteria, or via private prescription for £150 to £350 per month, depending on the provider.

Orforglipron is now available in the UK via private prescription. With Voy, pricing starts from £69 a month for the lowest dose on a 6-month plan.

NHS access will take longer, since it needs to go through a separate review. If it's eventually approved for NHS use, patients would pay the standard prescription charge (currently £9.90 per item in England, with prescriptions free in Scotland, Wales, and Northern Ireland).

Which is better: orforglipron or Mounjaro?

Mounjaro is more effective for weight loss based on trial data. People on the highest 15mg dose of Mounjaro lost up to 22.5% of their body weight over 72 weeks, compared to 12.4% for orforglipron at the highest licensed 17.2mg dose.

But the right choice depends on your circumstances:

• Mounjaro may suit you better if: you want the strongest weight loss results and don't mind weekly injections. It's the stronger option for people actively trying to lose weight.
• Orforglipron may suit you better if: you'd prefer a daily tablet, want to avoid injections, or are looking for a maintenance option after losing weight on an injection.

Once orforglipron (Foundayo) is available through Voy, our clinical team will support you in deciding what's right for you. At Voy, we currently offer Wegovy, the Wegovy pill, Mounjaro, and Orlos (orlistat) weight loss tablets.

Take our quiz to see which option might work for you, or join the waitlist for Foundayo and we'll let you know as soon as stock arrives.